X-rays are attenuated according to an X-ray attenuation coefficient, such as photoelectric effect, Compton scattering, and the like, of a substance placed in a path of the X-rays.
X-ray imaging modality is radiography using permeability of X-rays, in which an X-ray image of an inner structure of a subject is obtained based on an amount of attenuation that is accumulated in the process of the X-rays passing through the subject. To achieve this, an X-ray imaging device includes: an X-ray source emitting X-rays toward a subject; an X-ray sensor disposed to face the X-ray source with the subject therebetween, and configured to receive the X-rays having passed through the subject; and an image processor configured to produce an X-ray image of a field of view (FOV) by using a detection result of the X-ray sensor.
Meanwhile, recently, X-ray imaging modality is being replaced with digital radiography (DR) using a digital sensor thanks to the development of semiconductor and information processing technologies, and an X-ray imaging method has also been developed in various ways.
As an example, a dental X-ray panoramic image is obtained through following process: radiographing by moving the X-ray source and the X-ray sensor along a subject, namely, a jawbone of an examinee while the X-ray source and the X-ray sensor face each other; and showing a transmission image by joining the radiographs and spreading arrangement relationship of a tooth and a tissue therearound of a desired focus layer on a jawbone trajectory. To achieve this, the X-ray source and the X-ray sensor perform rotational movement along a rotating axis therebetween within a predetermined angular range, and perform linear movement in forward and backward directions of the examinee within a predetermined length range.
The X-ray panoramic image is used as a standard image, which is the most familiar to dentists, since the entire arrangement relationship of a tooth and tissue therearound can be easily identified. However, it is problematic in that to obtain the X-ray panoramic image, a multi-axis drive system is required to link the rotational movement with the linear movement of X-ray source and the X-ray sensor.
As another example, a dental X-ray computed tomographic (CT) image is obtained through following process: radiographing by rotating the X-ray source and the X-ray sensor along a subject, namely, a head of an examinee while the X-ray source and the X-ray sensor face each other; and showing a three-dimensional X-ray image of a field of view including the head by reconstructing the radiographs. To achieve this, the X-ray source and the X-ray sensor rotates along a rotating axis passing by a subject within a predetermined angular range while facing each other.
The X-ray CT image is capable of not only displaying a three-dimensional X-ray image of a subject, but also accurately and clearly displaying a tomographic image according to desired location and direction, whereby it is used in fields that require high precision, such as implant procedures, etc. However, it is problematic in that radiation dose irradiated to an examinee is high to obtain a general X-ray CT image, and an expensive X-ray sensor having a large area is required.
To be more specific to the latter, when performing a general X-ray CT, the sensor should receive X-rays of the entire area having passed through a field of view in all directions. Accordingly, a sensor having an area much larger than that of the sensor for a panoramic X-ray image is required.
As an example, in the case of obtaining an X-ray CT image of a field of view having a first height t1 and a first width w1 by using a cone beam X-ray imaging method that is mainly used in dental fields, assuming that the rotating axis between the X-ray source and the X-ray sensor passes by a center of the field of view, a second height t2 of the sensor should be the same as or more than a value of a magnification ratio*the first height t1 (that is, t2≥magnification ratio*t1), wherein magnification ratio is defined as a distance ratio of a distance between the X-ray source and the rotating axis to a distance between the X-ray source and the X-ray sensor; and a second width w2 of the sensor should be the same as or more than a value of the magnification ratio*the first width w1 (that is, w2≥magnification ratio*w1), whereby it is possible to receive the X-rays of the entire area having passed through the field of view. Here, if necessary, a half beam X-ray imaging method can be used, which is configured to reduce the second width of the sensor to a value of a maximum magnification ratio*(w1)/2 by using an asymmetric X-ray beam covering more than a half of the field of view.
However, regardless of the imaging methods, an area of a sensor for X-ray CT is large. Further, cost of a general sensor increases dramatically according to an area thereof, so an X-ray CT imaging apparatus is problematic in that a sensor having a large area is required. Accordingly, the cost thereof increases due to size of the sensor.